Hardening hollow cold extruded steel shaft

摘要

Hardening hollow shafts (especially drive shafts) of cold extruded 25 Cr Mo4 steel in an atmosphere containing nitrogen and carbon (formed by methanol and propane addition) involves: (a) heating at 930-980 deg C for 50-100 mins. at an atmosphere carbon level of 0.3-0.6%; (b) increasing the carbon level to 0.8-0.95% for 60-100 mins.; (c) rapidly reducing the carbon level to 0.6-0.75% at 930-980 deg C and holding for 60-100 mins.; (d) reducing the temperature to 820-890 deg C and holding for 40-130 mins; and (e) quenching in an oil bath at 60-90 deg C for 15-30 mins. Also claimed is a hollow drive shaft produced by the above method.